In today's world, in various vehicles having wheels such as a truck, a bus, a passenger car, and a motor cycle where tires are assembled in rims, there has been proposed installation of a tire inner pressure alarm system which always monitors tire inner pressure and notifies abnormalities of the tire inner pressure when necessary.
According to the tire inner pressure alarm system, for example, in a tire cavity area surrounded with an inner peripheral surface of the tire and a bottom surface of a rim bottom portion and filled with air, there are disposed a pressure sensor for measuring inner pressure, and a transmitter for transmitting inner pressure data measured by this pressure sensor by radio. Additionally, in the tire house vicinity of a vehicle body side, there is disposed an antenna of a receiver for receiving the inner pressure data, and the inner pressure data is received by this antenna. At the receiver, whether the tire inner pressure is abnormal or not is always monitored. In the case of an abnormality, a driver is notified of the inner pressure abnormality.
In this case, when the inner pressure data is transmitted from the transmitter to the receiver, a unique identification signal held by the transmitter is transmitted to the receiver, and the receiver can know which transmitter has transmitted the inner pressure data. Additionally, at the receiver, identification information of the receiver and wheel installation position information (information regarding right front wheel, right rear inner wheel, right rear outer wheel, left front wheel, left rear inner wheel, or left rear outer wheel) are correlated with each other to be registered in advance. The wheel installation position information is obtained from the identification information transmitted together with the inner pressure data by referring to a result of the correlation. Accordingly, it is possible to know the installation position of the wheel from which the inner pressure data has been transmitted.
On the other hand, for the tire assembled to the wheel, to prevent shortening of a tire life caused by uneven wear of a tire tread portion, so-called wheel rotation including the tire is carried out to change the wheel installation position for each specified traveling kilometers of the vehicle or according to need. In this case, as the transmitter is disposed in the tire cavity area to be fixed, during the wheel rotation, the wheel is. fixed to another installation position while the transmitter remains fixed. Thus, to correlate the identification information of the transmitter with the installation position of the wheel actually fixed to the vehicle after the rotation, correct installation position information after a change of a mounting position of the wheel must be provided to the receiver.
JP 3212311 B (Patent Document 1) and JP 2639856 B (Patent Document 2) each disclose a device for monitoring air pressure in tire and a remote tire pressure monitoring system.
The tire air pressure monitoring device disclosed in Patent Document 1 includes a pressure measuring device which is a pressure sensor, a transmission device which is a transmitter, and a receiver, and setting of correct installation information after wheel rotation is carried out in a paring mode (lines 8 to 42 in column 15 of Patent Document 1).
In the pairing mode of Patent Document 1, for example, each receiver disposed in the vicinity of an installation position of each wheel receives a signal having the maximum signal strength among signals transmitted from a plurality of transmitters. Thus, by correlating identification information unique to the transmitter contained in the received signal with an installation position corresponding to an installation position of the receiver which has received the signal, the identification information and a wheel installation position can be correlated with each other (lines 8 to 18 in column 15 of Patent Document 1). Moreover, by manually changing inner pressure for each wheel while checking to find inner pressure data having an identification signal which matches this inner pressure change at the receiver, the corresponding identification signal and the wheel installation position can be correlated with each other (lines 30 to 42 in column 15 of Patent Document 1).
On the other hand, according to Patent Document 2, the system includes a pressure sensor for detecting pressure, transmitting means which is a transmitter, and receiving means for receiving a signal, and a magnetic operation switch is mounted to the transmitting means. Further, the magnetic operation switch of the transmitting means is operated by moving a strong magnet near the wheel position to transmit a learning mode signal from the transmitting means to the receiving means. Accordingly, the wheel installation position is correlated with the receiving means (lines 6 to 13 in column 3 and lines 10 to 31 in column 11 of Patent Document 2).
Incidentally, in the pairing mode of Patent Document 1, at the receiver arranged in the vicinity of each wheel, correlation is carried out on the assumption that a signal having the maximum signal strength is a signal transmitted from the transmitter closest to the receiver. In many cases, however, a result of the correlation obtained in the pairing mode is not always correct. As the transmitter is mounted to a rotating rim or tire, directional property of a radio wave emitted when the transmitter transmits a signal causes a change in strength of the signal received by the receiver depending on the circumferential position of the transmitter around the rim in the pairing mode. Thus, in the paring mode implemented in a stationary state where traveling of the vehicle is stopped, the signal received by the receiver may not be a signal from the transmitter closest to each receiver but a signal from a transmitter disposed in each of adjacently installed wheels as in the case of a truck vehicle.
Reliable correlation is possible by checking to find an identification signal which matches the change of the inner pressure at the receiver while the tire inner pressure is manually changed with respect to each wheel. However, this is time-consuming troublesome work. Thus, working efficiency is low in a vehicle production line, causing a problem of a reduction in production efficiency. Further, also during wheel rotation, in the case of a large truck vehicle having a large number of wheels such as 12, work is troublesome because inner pressure is manually changed for each wheel.
According to Patent Document 2, the transmitting means includes the magnetic operation switch. Thus, when this transmitting means is mounted to a rotating wheel, the transmitting means is easily damaged by vibration or a centrifugal force which accompanies the rotation of the wheel, causing a problem of deterioration of durability.
Therefore, to solve the foregoing problems, an object of the present invention is to provide a highly durable wheel information-acquiring system capable of surely knowing from which wheel wheel information regarding a wheel received by a receiver has been transmitted and having no contact point such as a magnetic operation switch, and a wheel installation position information-setting device used for this acquiring system.